The overall objectives of the studies proposed in this application are to investigate the molecular pathways that sustain leukemia stem cells with the ultimate goal of defining novel cancer biomarkers and therapeutic targets. The proposed studies build on our recent discoveries that PGDH (NAD+-dependent 15-hydroxyprostaglandin dehydrogenase), a key enzyme involved in metabolic inactivation of prostaglandins, is implicated in the pathogenesis of a major subset of acute leukemia. It is highly expressed in leukemia stem cells, and serves as a crucial mediator in the MLL/HOX pathway that regulates leukemia stem cell self-renewal. The implicated role of PGDH is highly unexpected, as it has not previously been associated with contributing to cancer causation, which contrasts with earlier proposed protective roles. Even more unexpected, is our observation that the contributions of PGDH to leukemia pathogenesis are independent of its enzymatic activity, thus inferring that PGDH has a previously unknown non-canonical and novel biochemical function. We hypothesize that PGDH qualitatively regulates self-renewal to induce aberrant stem cell and/or progenitor expansion, a hypothesis that will be addressed in three specific aims. In Specific Aim #1, we will determine the mechanism for the non-canonical role of PGDH in leukemia pathogenesis. Using gain-of-function genetic approaches in mouse model systems, we will perform structure/function studies to identify leukemia-specific functional domains of PGDH. This will direct subsequent biochemical studies to identify proteins that specifically associate with essential domains required for PGDH oncogenic contributions. Studies in Specific Aim #2 will define the molecular pathways sustained by PGDH in leukemia stem cells using a combination of mouse models of acute leukemia as well as human leukemia cell lines and cells. The molecular pathways affected by PGDH will be characterized using high throughput expression profiling techniques, in conjunction with high-end bioinformatics to establish its role in human leukemia subtypes. In Specific Aim #3 we will define the role of PGDH in normal hematopoiesis using a genetic approach with a particular emphasis on hematopoietic stem cell maintenance and self-renewal in PGDH conditional knockout mice. A greater understanding of the non-canonical functions of PGDH in cancer versus normal stem cells will provide a unique biomarker and facilitate efforts to achieve more efficacious therapies by selectively targeting leukemia stem cells while sparing hematopoietic stem cells. PUBLIC HEALTH RELEVANCE: The studies in this application investigate a key molecular pathway that sustains leukemia stem cells, the crucial cell subpopulation responsible for maintaining cancers of the blood-forming cells. Particular emphasis will focus on a novel role in cancer stem cell function for an enzyme otherwise associated with prostaglandin metabolism, and not previously implicated in cancer causation. A greater understanding of the unique functions for this factor in cancer versus normal stem cells will facilitate efforts to selectively target cancers to achieve more efficacious therapies.